The invention relates to a field number conversion circuit for converting a television signal to be converted, having a first field frequency, into a converted television signal having a second field frequency, comprising a field memory circuit for writing therein, for each field the television signal to be converted, a read clock signal generator which is frequency-coupled to the horizontal deflection frequency of the converted television signal, a control circuit for controlling writing and reading of the memory circuit, a circuit for obtaining display synchronizing signals for the converted television signals and a correction circuit for obtaining for each field, according to the position of the television signal to be converted in an associated picture, a corresponding position of the converted television signal in an associated picture.
"Elektronica", 1982, No. 4, pages 27-33 discloses a field number conversion circuit of the above-described type, in which the frequencies of the clock signals and of the synchronizing signals are coupled to each other and the correction circuit applies an additional deflection current to the vertical deflection coils for correcting, for an interlaced picture, the converted television signal in the picture to be displayed. This conversion circuit is only suitable for converting standard signals having a fixed number of interlaced fields and lines.